Investigations on vertebrate motor control will be concerned with vestibulospinal reflexes, with originating in neck receptors and acting on the limbs or body, and with the organization of the upper cervical spinal segments. A principal goal of the vestibulospinal work will be to study neural circuitry underlying functionally meaningful reflexes. Complex, as well as short latency, pathways between labyrinth and forelimb motoneurons will be studied by activating vestibular afferents by electric stimuli or by sinusoidal polarization. The behavior of vestibular neurons projecting to the forelimb segments and of interneurons in these segments in response to such stimuli will be examined by single-cell recording. We will try to determine, by spike-triggered averaging, whether excited interneurons project to motoneurons. The dynamics of otolith reflexes of neck and forelimb muscles will be studies with a computer-controlled tilt table; EMG and single brainstem neuron activity will be recorded. In the second project the goal is to study the circuitry underlying neck reflexes. We will do this by looking at the effect of activation of proximal, and distal, neck afferents on spinal neurons. We will record intracellularly and extracellularly from motoneurons and interneurons respectively in the forelimb segments. Convergence between vestibular and neck input will be examined. In the third project we will use electrophysiological techniques to study some aspects of the organization of the upper cervical segments. With intracellular recording we will study the reflex effects of afferents in the region of the neck joints on neck motoneurons. We will also investigate divergence of afferents from spindle primaries; many neck muscles are innervated from several spinal segments and we will test the effectiveness of afferents in one segment on motoneurons in the same and other segments.